CONCRETE LINING FOE IRRIGATION CANALS. 85 
CARE TO BE EXERCISED IN OPERATION. 
The durability of concrete lining for canals depends not only on 
good construction but on the care given it as well. Sudden changes 
of temperature, such as turning out cold water and exposing a lined 
channel to a hot sun, damage from roots of trees, damage from stock 
and storm water, the formation of ice, etc., may be very injurious 
and destructive to good construction unless proper precautions are 
taken. 
The flow in the Davis and Weber Counties Canal in Utah some 
years ago had been turned out in the early spring when the water was 
cold. The effect of a hot sun on the concrete lining caused it to 
expand and buckle in a few places. The lining had been amply pro- 
vided with expansion joints, but the wooden cleats used during con- 
struction had not been removed. No harm would have resulted if 
the strips had been removed and the joints filled with asphalt. This 
instance is mentioned to show how injury may occur through care- 
lessness in construction and operation. In such connection can be 
seen the benefits arising from the use of a somewhat lean mortar for 
the finishing coat and thus avoid as much as possible the shearing 
effect between the base of the lining and the surface coat due to the 
inequality of their coefficients of expansion. 
The growth of trees along or near the banks of a canal may injure 
a concrete lining by the displacement or breaking of individual slabs. 
The possibility of such injury may be guarded against during con- 
struction by entirely removing or cutting back and deadening the 
tree growth. 
Fencing the right of way is the only remedy against damages caused 
by stock. 
Any storm water which is likely to be discharged into the canal 
should be bypassed. A cloudburst or heavy rainstorm may so raise 
the height of water in the canal as to endanger its safety, and the flow 
from even small volumes of storm water entering a canal is usually 
destructive to the upper part of the lining by washing away the earth 
backing. 
If it becomes necessary to operate a concrete-lined canal in freezing 
weather, every precaution should be taken to avoid injury that may 
arise through the formation of ice. One of the principal rules to be 
observed is to increase, rather than diminish, the flow prior to the 
beginning of the ice-forming period. The writer has discussed the 
operation of canals in winter elsewhere. 1 
The formation of ice in a concrete-lined canal is not necessarily 
injurious. In such instance the canal should be operated to obtain 
a condition as mentioned in the preceding paragraph and referred to 
U. S. Geol. Survey Water-Supply and Irrig. Paper 43 (1901). 
